Bacteria are responsible for a significant amount of disease and infection. Ridding surfaces of bacteria is desirable to reduce human exposure. Because bacteria have developed self-preservation mechanisms, they are extremely difficult to remove and/or eradicate.
Bacteria can be found in several forms, including planktonic and biofilm. In a biofilm, bacteria interact with surfaces and form colonies which adhere to a surface and continue to grow. The bacteria produce exopolysaccharide (EPS) and/or extracellular-polysaccharide (ECPS) macromolecules which crosslink to form matrices or films that help to keep the bacteria attached to the surface
In addition to adhering to surfaces, biofilm matrices protect bacteria against many forms of attack. Protection likely involves both the small diameter of the flow channels in the matrix, which restricts the size of molecules that can transport to the underlying bacteria, and consumption of biocides through interactions with constituent EPS and/or ECPS macromolecules.
Additionally, bacteria in biofilm form are down-regulated (sessile) and not actively dividing. This makes them resistant to attack by a large group of antibiotics and antimicrobials, many of which attack the bacteria during the active parts of their lifecycle, e.g., cell division.
Due to protection afforded by the macromolecular matrix and their down-regulated state, bacteria in a biofilm are very difficult to treat. The types of biocides and antimicrobials that can effectively treat bacteria in this form are strongly acidic or oxidizing, often involving halogen atoms, oxygen atoms, or both. Common examples include concentrated bleach, strong mineral acids (e.g., HCl), high concentrations of quaternary ammonia compounds and aldehydes, and H2O2. Commonly, large dosages of such chemicals are allowed to contact the biofilm for extended amounts of time (up to 24 hours in some circumstances), which makes them impractical for many applications.
Formulations that disrupt the macromolecular matrices or bypass and/or disable the defenses inherent in these matrices have been described in U.S. Pat. Publ. Nos. 2010/0086576 and 2012/0059263. These formulations are aqueous compositions containing an acid or base, a buffering salt added at sufficient concentration to yield a relatively high osmolarity, and large amounts of surfactant, with the solutes creating an osmotic pressure differential across the bacteria cell wall and the surfactant(s) weakening those walls by interacting with wall proteins.
The foregoing compositions usually do not immediately break down the biofilm macromolecular matrix and, instead, transform that matrix into a gel-like state, which still provides some shielding of the bacteria. The aggregate efficacy and disinfection rate of these compositions thus are limited by the flux rate of the active ingredient(s) moving through the biofilm matrix and rate of bacterial cell wall degradation. (Disruption of the EPS decreases the mean free path that the antimicrobial components must travel.)
Further, regulatory bodies such as the U.S. Food and Drug Administration and Environmental Protection Agency have set threshold amounts for surfactants such as benzalkonium chloride and cetylpyridinium chloride. Any composition that includes such surfactants in amounts above those thresholds must be reviewed for safety prior to commercial introduction for certain applications such as, but not limited to, food contact (without rinsing), oral rinses, medical instrument sterilization, and skin contact. The foregoing compositions have surfactant concentrations that usually exceed regulatory threshold amounts.